The present invention relates to a layout of a semiconductor integrated circuit, and more particularly to a layout of a semiconductor integrated circuit wherein resistance-capacitor (RC) filter circuits are integrated with analog circuits and digital circuits. The resultant layout enables the semiconductor integrated circuit to effectively deal with surges and noises.
In recent years, to deal with electromagnetic wave noises in semiconductor integrated circuits, some integrated circuit (IC) chips have been provided with filter circuits for cutting electromagnetic wave noises from outside. For example, in IC chips for use in automobiles and the like, a single stage RC filter comprised of a resistance and a capacitor or a multistage RC filter such as a secondary filter is connected to a power supply line or an input/output signal line in an integrated circuit.
Since the RC filter is connected to the power supply line or input/output signal line in the integrated circuit, however, a surge is likely to be applied to the RC filter via a pad connected to the line. If the surge is applied to a high voltage side electrode of a capacitor constituting the RC filter, electric fields are concentrated between the electrode and peripheral circuit elements or lines. This may cause dielectric breakdown of the capacitor to break the filter circuits.
Further, since the electrode of the capacitor constituting the RC filter is formed in a wide area on the IC chip, the electrode of the capacitor tends to be positioned close to analog circuits and digital circuits in a layout of the integrated circuit. In such a layout, when a noise is superimposed on the electrode of the capacitor, the noise is likely to be transmitted to peripheral circuits to cause malfunction thereof. Namely, the integrated circuit will not withstand the noise. Also, the application of the surge has a significant effect, and is likely to cause latch-up and dielectric breakdown of the peripheral circuits.
To improve the performance against the noise and surge, several approaches have been developed. Using an insulation layer with high dielectric resistance and low dielectric constant is one of them. However, a special material used for the insulation layer requires a high development cost and a long optimization time, and it is necessary to solve issues on productivity and other potential risks.
It is therefore an object of the present invention to provide a layout of a semiconductor circuit wherein an RC filter for cutting electromagnetic wave noises is integrated with analog circuits and digital circuits, and the layout improves the capability to withstand noises and surges with a relatively low cost and short turnaround.
To accomplish the above object, the present invention provides a layout of a semiconductor integrated circuit in which an RC filter for eliminating electromagnetic wave noises is integrated with analog circuits and digital circuits on the same circuit board. In the semiconductor integrated circuit, a high voltage side electrode of a capacitor constituting the RC filter is disposed apart from a circuit element or line of the analog circuits and digital circuits at such an interval as to prevent the circuit element from malfunctioning due to a noise superimposed on the high voltage side electrode or to prevent dielectric breakdown of the capacitor, latch-up or dielectric breakdown of the circuit element caused by a surge applied to the high voltage side electrode. Specifically, the interval between the high voltage side electrode of the capacitor constituting the RC filter and the circuit element or line of analog circuits and the likes positioned closest to the RC filter is not less than a minimum interval required by a layout rule, or is five times longer the minimum interval required by the layout rule if a safety margin is considered.
According to the present invention, the high voltage side electrode of the capacitor constituting the RC filter is disposed apart from circuit elements or lines constituting analog circuits and digital circuits at such an interval as to prevent the circuit element from malfunctioning due to the noise superimposed on the high voltage side electrode or to prevent dielectric breakdown of the capacitor constituting the RC filter and latch-up or dielectric breakdown of the circuit element caused by the surge applied to the high voltage side electrode.
If the RC filter is a secondary or a higher stage filter in the layout according to the present invention, it is preferred that a high voltage side electrode of the primary side filter capacitor, which is most susceptible to a noise and surge from outside among all capacitors constituting the RC filter, is positioned apart from circuit elements or lines constituting the analog circuits and digital circuits at such an interval as to prevent malfunction of the circuit elements caused by the noise superimposed on the high voltage side electrode or to prevent dielectric breakdown of the capacitor constituting the RC filter and latch-up or dielectric breakdown of the circuit elements caused by the surge applied to the high voltage side electrode. Here, the primary side filter capacitor is a capacitor that is positioned closest to the pad on the chip that a line noise or the like enters.
According to the present invention, in the case where the RC filter constitutes a secondary or a higher stage filter, the high voltage side electrode of the primary filter capacitor is disposed apart from circuit elements or lines constituting the analog circuits and digital circuits at such an interval as to prevent malfunction of the circuit elements caused by the noise superimposed on the high voltage side electrode or to prevent dielectric breakdown of the capacitor constituting the RC filter and latch-up or dielectric breakdown of the circuit elements caused by the surge applied to the high voltage side electrode.
Further, if the RC filter constitutes a secondary or a higher stage filter, capacitors are arranged inward from the periphery to inside of an IC chip; for example, a primary filter capacitor is disposed at the outer periphery of the IC chip, a secondary filter capacitor is disposed inside the primary filter capacitor, and a tertiary filter capacitor inside the secondary filter capacitor. Circuit elements other than the RC filter are arranged at the innermost side of the chip.
According to the present invention, the primary filter capacitor is disposed at the outer periphery of the IC chip, the secondary and higher stage capacitors are arranged in the order of stage inside the primary filter capacitor, and the circuit elements other than the RC filter are arranged at the innermost side of the IC chip.